1. Field of the Invention
The present invention relates to an automatic focusing system wherein plural points in a field of view framed by a lens are available for detecting the focus state of the lens, and any one of those points can be selected as a targeted point to be in-focus. This invention can be adequately embodied in still cameras, video cameras, or any other types of cameras.
2. Related Background Art
Various automatic focusing systems have been proposed wherein plural points in a field of view are available for detecting the focus state of a lens or measuring a distance to a subject from a camera, and some of those points are selected as a targeted point to be in-focus. For example, in an active automatic focusing system with the rangefinder, three to five different beams from infrared-emitting diodes are available. Each beam independently provides measurement of the camera-to-subject distance and the measured results are compared and analyzed to determine which beam points to the object a photographer wants to take a picture of. This beam is taken and the information on the distance measured by that beam is used to adjust the lens for focusing.
In this type of system, automatic focusing is achieved no matter where the image of the object is in the field of view. Thus, this system gives a photographer the advantage that he can concentrate on his artistic work such as composing the picture.
The single-point-focus-detection automatic focusing systems have the disadvantage that a photographer has to place the focus-detection point over the subject in the viewfinder. Otherwise automatic focusing does not work.
On the other hand, multi-point-focus-detection automatic focusing systems have the advantage that a photographer can freely make any composition of a picture with no special techniques such as autofocus locking.
The multi-focus-detection-point automatic focusing system has been adopted to single-lens reflex cameras. In the passive system, natural light from the subject is used for automatic focusing and distances from the camera to plural different points on the subject are measured. Evaluation of the measured distances to the plural points is carried out to determine or speculate the which point a photographer aims. Thus, one point is taken and the information on the distance to that point is used to adjust the lens and control the focusing state.
The present inventor presented such an automatic focusing system described above in Japanese Patent Application Laid-Open Nos. 1-288810 and 1-288813. In Japanese Patent Application Laid-Open No. 1-288810, was disclosed the automatic focusing system comprising an optical system which provides plural focus-detection points and plural sensors arranged adequately. In Japanese Patent Application Laid-Open No. 1-288813, was disclosed the method to select a point properly from the plural focus-detection points.
Single lens reflex cameras are often expected to provide the capability to achieve any composition of a picture in conjunction with the good technique of a photographer. In order to realize such a requirement, it must be possible that the photographer himself selects any focus-detection point as a targeted point to be in-focus according to his intention, instead of the automatic focusing system.
The intentional selection of the focus-detection point by a photographer is very important especially when a camera is mounted on a tripod, because autofocus locking does not work in this case. Also, in the case where there are some obstacles between the main subject and a camera, intentional selection by the photographer is needed because it is difficult for the camera to distinguish what is the real subject to which the photographer aims. The present inventor proposed, in Japanese Patent Application No. 2-260839, the camera system which has means for intentional selection and a display to indicate to which point is selected for confirmation.
As described just above, there are two ways to select a proper point (or an otherwise small number of points) from the plural focus-detection points for adjusting the lens. One is the automatic selection and the other is intentional selection by a photographer. Some cameras provide both the means of intentional selection and automatic selection, but they have the following problems:
When selection is done automatically, it is desirable that there are as many focus-detection points arranged as densely as possible. These points must be arranged densely enough so that some point can automatically hit the subject no matter where the subject is in the field of view. The automatic selection must be possible with no care by a photographer, in fact, many cameras have no display to indicate a targeted point. As explained just above, too small density of focus-detection points leads to the high risk that no point hits the subject. High density points, or almost continuously arranged points are desirable so that some point can hit the right subject to which a photographer aims, under whatever conditions, independently of the subjects, the distance between the subject and the camera, the exchanging of lenses, or the zoom ratio.
On the other hand, when the focus-detection point is selected intentionally by a photographer, it is desirable that the points are distributed at the proper space, because too short of a spacing between the neighboring points causes troublesome selecting operation with no significant practical advantage. Moreover, when the point is selected by a photographer, there must be some means to show the photographer where the targeted point is. It is desirable that displays for that purpose are in the viewfinder. If there are too many or too dense displays, it is difficult for a photographer to distinguish the displays. It is also difficult to give high enough brightness to many displays. From these points of view, the adequate number of the focus-detection points in the horizontal direction is three to five, or the adequate space between each point is 5 to 6 for the 35-mm films. For the vertical direction, three points are enough.
As discussed above, the adequate arrangement or adequate number of the points depends on whether the point is selected intentionally by a photographer or by a camera itself automatically. Therefore, there has been a difficult problem of how to realize two different arrangements of focus-detection points in a camera at the same time.